1. Field of the Invention
This invention relates to electronic circuits, and more particularly, to ring oscillators.
2. Description of the Related Art
Ring oscillator circuits are well known in the art of electronics. Common ring oscillators may be constructed of an odd number of inverters coupled in a chain, with the output of a last inverter in the chain fed back to the input of a first inverter. Such a configuration results in a circuit that, when a sufficient voltage is applied, oscillates spontaneously between two logic voltage levels (i.e. a high level and a low level).
Ring oscillators have a variety of applications, such as clock signal generation and temperature sensing. Complementary ring oscillators, a variation of the traditional ring oscillator, may be used in applications where complementary outputs are desired.
The particular frequency at which such a circuit oscillates is determined by various factors, such as the transistors used to implement the various elements. Due to the demands of higher clock speeds and smaller feature sizes, implementation of ring oscillators has become more difficult. In particular, at higher frequencies and smaller feature sizes, degradation mechanisms such as noise susceptibility and jitter become problematic. In addition, complementary ring oscillators designed on differential amplifier circuits may have a relatively large footprint and may consume more power than their single ended counterparts, while producing output signals that are not full-swing (and thus require additional buffers). Therefore, designing complementary ring oscillators having a high frequency output that is full swing with good noise immunity and low jitter provides a difficult challenge.